Air Pollution Impacts

Big Bend National Park

Natural and scenic resources in Big Bend National Park (NP) are susceptible to the harmful effects of air pollution. Fine particles, nitrogen, ozone, and toxics impact scenic resources such as visibility, and natural resources such as surface waters, fish, and vegetation. Click on the tabs below to learn more about air pollutants and their impacts on natural and scenic resources at Big Bend NP.

Visibility

Nitrogen & Sulfur

Ozone

Toxics & Mercury

Air pollutants can affect visibility at Big Bend NP, Texas (clear to hazy from top to bottom).

Many visitors come to Big Bend NP to enjoy panoramic vistas of the ribbon-like Rio Grande, or endless miles of Chihuahuan Desert. Unfortunately, these vistas are often obscured by haze caused by fine particles in the air; oftentimes the result of nearby coal-burning power plants. Many of the same pollutants that ultimately fall out as nitrogen and sulfur deposition contribute to this haze and visibility impairment. Organic compounds, soot, and dust reduce visibility as well.

Visibility effects at Big Bend NP include:

Reduction of the average natural visual range from about 160 miles (without the effects of pollution) to about 70 miles because of pollution at the park;

Reduction of the visual range from about 120 miles to below 40 miles on high pollution days;

Sulfate particles are the single largest contributor to haze at the park. Sources of this secondary pollutant include coal-fired power plants, metal smelters, refineries, other industrial processes, and volcanoes (Pitchford et al. 2004).

Episodes of high pollution at the park are the result of emission from sources in East Texas, the Gulf Coast (Houston and Galveston) and U.S. states further to the north and east, as well as northeastern Mexico (Monterrey and Monclova) and Mexico City (Pitchford et al. 2004).

Surface waters and soils at Big Bend NP in Texas are well-buffered against acidification from nitrogen and sulfur deposition.

Nitrogen (N) and sulfur (S) compounds deposited from air pollution can harm surface waters, soils, and vegetation. N and S deposition cause acidification of streams and lakes in some parts of the country, while N deposition is known to disrupt soil nutrient cycling and alter aquatic and plant communities. Surface waters at Big Bend NP are likely to be well-buffered from acidification because of an abundance of base cations like calcium in the soils and rocks. However, arid, upland areas in the park are sensitive to fertilization from excess nitrogen. The sparse native vegetation in the park is not adapted to higher nitrogen levels and therefore may be displaced by invasive species like cheatgrass. Such non-native species can readily take up nitrogen and use it to their advantage.

Naturally-occurring ozone in the upper atmosphere absorbs the sun’s harmful ultraviolet rays and helps to protect all life on earth. However, in the lower atmosphere, ozone is an air pollutant, forming when nitrogen oxides from vehicles, power plants, and other sources combine with volatile organic compounds from gasoline, solvents, and vegetation in the presence of sunlight. In addition to causing respiratory problems in people, ozone can injure plants. Ozone enters leaves through pores (stomata), where it can kill plant tissues, causing visible injury, or reduce photosynthesis, growth, and reproduction.

Big Bend NP has several ozone-sensitive plants including Rhus trilobata (skunkbush) and Pinus ponderosa (ponderosa pine). Ozone concentrations and cumulative doses are at levels in the park known to cause injury to such sensitive plants. However, the generally dry conditions in the park cause increased plant pore (stomatal) closures, thereby reducing ozone uptake by plants and the injury that results.

Birds of prey, such as the peregrine falcon, at Big Bend NP in Texas show elevated levels of DDE (a breakdown product of DDT) and mercury.

Toxics, including heavy metals like mercury, accumulate in the tissue of organisms and may alter key ecosystem processes. When mercury converts to methylmercury in the environment and enters the food chain, effects can include reduced reproductive success, impaired growth and development, behavioral abnormalities, reduced immune response, and decreased survival. Human activities have greatly increased the amount of mercury in the environment through processes such as burning coal for electricity and burning waste. Other toxic air contaminants of concern include pesticides, industrial by-products, and emerging chemicals such as flame retardants for fabrics. Some of these toxics are also known or suspected to cause cancer or other serious chronic health effects in humans and wildlife. Such environmental toxins present a concern for natural resources as well as park visitors and locals who fish for pleasure or sustenance.